Conventional focusing apparatus for a lens system involving telescopes, microscopes, cameras and the like includes the lens system mounted in a framework, ordinarily a tube, and a transversely mounted adjusting mechanism to focus the lens system on the object to be observed or photographed. Numerous systems have used a rack and pinion or gear systems to move the lens system to the proper focus. The problem is that a gear system inherently includes a frictional relationship and a back lash due to material stress is inherent. Such back lash can make the best focus a difficult chore for the observer.
An example of an early focusing mechanism is in U.S. Pat. No. 1,120,014 showing a rack and pinion operation including gears as a mechanism for adjusting the focus of a lens system.
U.S. Pat. No. 1,521,067 is a modification of a lens adjusting system involving overlapping offset bands of woven material used to translate the lens system into the desired focus.
U.S. Pat. No. 1,576,340 shows a transverse offset mechanism for a lens system involving rollers riding on a rail and engaging alternate rollers to swing the lens system focus up and down or to one side or the other.
U.S. Pat. No. 3,768,885 involves a microscope. For focus adjustment a mechanical linkage and a rotatable cam are combined with a gear train. The whole system is much more complicated than necessary.
U.S. Pat. No. 4,204,732 describes adjusting the focus of a lens system by the use of gears. The inherent back lash problem is well known and undesirable.
U.S. Pat. No. 4,591,245 discloses adjusting the focus of a lens system using a threaded rod combined with a cam or lever system to move the lens system. Threads serve essentially the same function as gears in the above described patents and do not eliminate the undesirable back lash.
A column in the May, 1986 journal, Sky & Telescope, at pages 511-513 describes a focusing apparatus involving a lens mounted in a tube. A flat area on the tube exterior is aligned with a rubber tube surrounding a focusing shaft. Rotation of the shaft moves the tube to the desired focus location.
Another column in the January, 1987 journal, pages 95-96 describes a similar focusing technique, but in the latter case a rubber strip is adhesively bonded to the tube in place of the flat area described in the May, 1986 column.
An article from the journal, Machine Design, of Dec. 21, 1967 describes the dynamic features of a flexible band threaded in S-shaped configuration around two rollers and anchored to a pair of plates. The plates are aligned in parallel with each other and perpendicular to the axes of the rollers. The initial tension of the band is sufficient to capture the rollers for non-slip movement thereof.